1. Field of the Invention
The present invention relates to a prosthetic heart valve anchor and a minimally invasive method for implantation.
2. Description of the Prior Art
It has been estimated that up to 20% of all cardiac surgeries are directly related to valve replacement or implantation of artificial valves. It is well known that a variety of medical conditions and diseases may cause damage to the heart valve which ultimately necessitates valve replacement. Certain diseases such as rheumatic fever can cause the valve orifice to shrink or pull apart. If these defects are not corrected, prolonged valvular stenosis or insufficiency may cause damage to the heart muscle and may even require complete valve replacement. Other indications, including congenital anomalies and myocardial infarction, may necessitate total valve replacement as well.
When complete valve replacement is necessary, the surgeon may choose from two types of prosthetic valves, mechanical or tissue valves. Mechanical valves are generally made from some type of rigid metal or hard plastic. They have been known to be formed from titanium coated with a pyrolytic carbon with polymer and biocompatible cloth covered sewing rings. Most of these currently available mechanical valves are either of a pivoting hi-leaflet or tilting mono-leaflet design. However, more flexible or elastic valves may be achieved using synthetic polymers which simulate a biological tissue valve.
Tissue valves, in contrast, consist of chemically preserved or cryopreserved animal tissue including human homografts and xenografts usually extracted from a pig or cow and typically mounted on a supporting frame known as a “valve stent”. The valve stent itself is constructed from a metal and polymer material and covered with a biocompatible cloth material. A sewing ring is then used to tether the valve to the annulus. The sewing ring is typically a tubular synthetic structure which is designed to allow passage of the suture through the sewing ring in order to tether the valve. The sewing ring may be comprised of a biocompatible cloth which covers a silicone sewing ring and further having three valve stent commissure posts which project upward from the cloth and which serve to hold the three tissue leaflets of the valve in proper placement. Additionally, the valve stent provides a structural integrity which enables the surgeon to insert and mount the valve into the heart and suture it into place. These tissue valves are inherently advantageous because they are less likely to cause thrombosis, thereby reducing the necessity of having the patient treated with anticoagulants. However the failure rate of these bioprosthetic valves is at 15% by fifteen years after surgery, and therefore these tend to require periodic replacement.
While heart valve implants have become widely accepted in the medical field, this procedure is still extremely costly. The medical personnel necessary for the procedure must comprise a skilled surgeon, perfusionist, anesthesiologist and a full operating room staff, as well as equipment which include a sophisticated heart/lung bypass machine. In addition to the expensive personnel, valve implant surgery requires extensive operating time which is both costly and subjects the patient to a greater health risk the longer he is on a bypass machine and under anesthesia.
It is the generally accepted practice in the medical field to implant prosthetic heart valve devices by means of surgical suturing of the valve into the heart. Valve designs currently on the market make the suturing technique advantageous because they permit direct securing of the valve with precise and easy visualization of the suture line. While there are a variety of advantages to this standard means of sewing the heart valve into orthotopic or heterotopic positions, there still remain a vast number of disadvantages which make an alternative means desirable to find. The sewing ring used to suture the valve into the patient's heart occupies a significant annulus area and therefore effectively reduces the amount of valve orifice area. Furthermore, suture placement itself can be a tedious process which often demands a significant portion of the overall operation time. This is especially true in the case of younger or small patients as well as those patients who have undergone repeat procedures. Based on the need to reduce the overall length of time a patient undergoes surgery, one can appreciate that reduced suturing time or removal of the suturing process altogether is highly advantageous.
In addition, the accepted practice of hand suturing traditional prosthetic heart valves into place requires large open access to the chest cavity to enable the surgeon to precisely suture the valve into the heart muscle. Access is usually made through the open chest and a longitudinal incision in the ascending aorta is typically utilized for handheld instruments utilized for both valve placement and suturing. Accurate placement and orientation of the valve within the heart is a difficult and high risk aspect of this procedure which may be minimized by enlarging the chest openings, giving the surgeon better access and increasing the prospect that the valve will be placed successfully. For most cardiovascular surgeries, the need for precise suturing for securement of the heart valve prosthetic has been difficult to improve upon.
Therefore, while adequate access to the chest cavity has been considered necessary during heart valve replacement, it is an extremely traumatic event for the patient and subjects them to a higher risk of infection. Thus it can be appreciated that the need exists for a heart valve prosthetic that is subject to placement using minimally invasive surgical techniques.
Additionally, suturing the prosthesis valve into the heart muscle creates a subsequent problem for the patient due to the fact that the valve itself is bulky, and when sutured into place, the suturing process necessarily reduces the cross section of the flow path through the valve body. Such a flow restriction may adversely affect blood flow which may increase the transvalvular pressure gradients of the heart thereby requiring it to work harder to pump the same volume of blood. For a patient already experiencing heart stress, the increased pressure on the heart is clearly undesirable.
In addition to the restriction within the heart valve itself, narrowing of the valve structure is often brought on by the surgeon pulling the sutures as snugly as possible during placement of the prosthetic. The more snugly the valve fits the better. However, the result is that the tissue becomes constricted at the site of the implant. Another problem with the suturing technique is a tendency to constrict the heart annulus. Constrictions occur when sutures draw the heart annulus upwardly toward the valve sewing ring thereby drawing it partially into the annular opening of such sewing ring. Other problems associated with suturing of the valve prosthetic occur when the suture is placed too deeply into the muscle wall. When the suture extends deep into the muscle wall, the suture can catch the back wall of a contiguous structure thereby causing damage to that tissue or otherwise injuring the cardio-conduction system which may result in conduction abnormalities. Similarly, the relationship between the leaflets and the cloth covering of the stent in biological tissue valves promotes pannus fibrosing tissue depositing, which eventually creeps inward from the periphery of the valve.
Similarly, sutures securing a valve in place may cause the formation of blood clots due to the presence of additional foreign objects in the body The danger caused by these blood clots can be severe if a clot breaks away and enters the patient's blood stream, thereby causing a major health problem such as a heart attack or stroke. Additionally, the very nature of sutures creates problems because when the surgeon stitches the sew cuff in place, he or she knots and cuts the thread leaving raw edges somewhat exposed to the patient's blood stream. These raw edges create another area of potential blood clot formation and infection. Due to the location of these potential blood clots, a formed clot may even extend into the valve itself thus trapping it open or shut and generally causing overall valve malfunctions. It has been the general practice to administer an anti-coagulant such as heparin or warfarin to post-surgical patients in an attempt to reduce this potential for blood clotting. However, it can be appreciated that a valve prosthetic. which itself does not produce blood clots, is a safer and overall better alternative than administration of a blood thinning drug. It has also been observed that the presence of foreign materials in the body, such as sutures and staples, increases the potential for bacterial injection at that site. Therefore the benefit of reducing the suture requirement becomes apparent.
While there is an obvious need to provide a sutureless heart valve prosthetic, such a valve must also still fit snugly and securely in the heart annulus. Without a secure fit between the prosthetic and the tissue, leaks may develop between the valve anchor and heart annulus thereby allowing blood to bypass the valve. Such a situation may be disastrous. Therefore, while a need exists to find a viable alternative to suturing, the valve anchor must securely attach to the heart muscle without exhibiting leakage.
Many efforts have been made over the years to provide a satisfactory anchoring ring for a prosthetic valve and a tool for placement thereof. One such effort focused on the problems associated with suturing. A cuff was proposed having an exterior fabric skirt connected therewith to be stapled to the native annulus to anchor the cuff in position. A rather elaborate tool was proposed for implanting the cuff and stapling the skirt to the annulus. Devices of this type are shown in U.S. Pat. No. 5,716,370 to Williamson et al. Such devices, while offering interesting solutions, are relatively complex and have not gained general acceptance in the field. Furthermore, the use of staples instead of sutures has been known to exhibit similar scarring and tension effects.
Another effort to create a secure valve holder which is also capable of reducing potential damage to the heart tissue was proposed as an assembly including a heart valve having a plurality of radially inwardly deflectable supports and a holder having inner and outer members for suture attachment and to ensure a counterbalancing of the suture tension. A device such as this is disclosed in U.S. Pat. No. 4,865,600 to Carpentier et al. While relatively effective in solving certain problems, such an assembly is fairly large and cumbersome as well as being mechanically complex.
Other devices for implanting a heart valve have been proposed which include a fork shaped tool having projecting tines which are flexibly mounted and formed on their distal ends with hooks which may be spread radially outwardly to releaseably hook into the interior of the cuff and be biased in position by a removable biasing spring which may be removed after implantation. A device of this type is shown in U.S. Pat. No. 5,236,450 to Scott. A device of this nature, while effective to grip a conventional cuff, does not provide for mechanical anchoring of the cuff to the annulus or provide for an arrangement for deployment of a mechanically anchoring device.
Therefore, it is clear that the need exists for a novel heart valve placement system which permits the surgeon to quickly, easily and securely implant the heart valve into the patient with minimal resulting trauma to the patient and yet which is simple to construct and use and which achieves a high level of success.